Does intermittent fasting preserve muscle mass during weight loss? A new study claims it does. This is quite exciting, so I'm interrupting my planned schedule to give you the low down on these findings. I just got access to this paper and I'll be writing this post as I read through it.

Right off the bat, let me note that the title and abstract does not mention intermittent "fasting" anywhere. Instead, the author is using intermittent "calorie restriction" (CR) as a catch-all term for various intermittent fasting regimens. This includes intermittent fasting (IF) and alternate-day fasting (ADF). Below I've listed the studies for intermittent CR included in the review:

Note the one study that is not published yet and includes exercise. I'm very much looking forward to seeing that one. It would be interesting to see what kind of exercise regimen they are using. I'm hoping it's weight training. So far there is a severe lack of intermittent-fasting-based studies that include exercise and not one that includes weight training. I'm talking long-term trials and not acute experimental trials like the one I talked about here: "Fasted Training Boosts Muscle Growth?"

The aforementioned studies all involve fasting, with time-intervals ranging from 18 to 36 hours. The modified ADF/CR-regimens involve one day of very low calorie intake, 300-800 kcal, followed by one day of ad libitum feeding (which means that participants were free to eat whatever they wanted).

So that's that. Not strict fasting as in "0 kcal" in a few of those studies but the energy deficit during the fasting days was quite severe. For the sake of simplicity, I'm going to use intermittent fasting (IF) when I refer to the various fasting-based regimens used in the study review. It gets damn confusing with "intermittent CR" when people are used to thinking of it as intermittent fasting - which is exactly what it is, with the exception of the modified ADF-regimens that are super-low calories every other day.

The physiological effect is probably not much different as it pertains to modified fasting regimens versus strict fasting regimens. I think the benefits of intermittent fasting is likely mediated by the cyclical nature of the meal pattern itself; a period - the fast - spent in an energy deficient state, followed by a brief period of an acute energy surplus - the feeding phase. More on that some other time. For a brief review of popular approaches to intermittent fasting, you might want to have a look at this post:

This is a review, which basically means a "study of studies", where the author, Varady, attempts to draw a conclusion from the collection of evidence available. Specifically, the author examined results from weight loss studies with intermittent fasting and compared those to weight loss studies with traditional calorie restriction. This sums up the objective of this review:

What has yet to be determined, however, is whether one of these interventions produces superior changes in body weight and body composition parameters when compared to the other. Accordingly, the objective of this review was to evaluate and compare the effects of daily CR versus intermittent CR on weight loss, fat mass loss, lean mass retention and visceral fat mass reduction, in overweight and obese adults.

The author then provides some basic data and background facts about the effects of weight loss on biomarkers, the various diets and their treatment periods, typical results, and so forth. Nothing too exciting. This little tidbit is worth mentioning:

When an individual loses weight by dietary restriction alone, approximately 75% of weight is lost as fat mass, and 25% of weight is lost as fat free mass (31). Fat free mass is an important predictor of basal metabolic rate (32). Thus, dietary interventions that preserve fat free mass at the expense of fat mass may be metabolically advantageous.

We were also interested in comparing the ratio of fat mass to fat free mass lost with intermittent CR versus daily CR. From the studies reviewed here, it would appear as though a lower proportion of lean mass is lost in response to intermittent CR (90% weight lost as fat, 10% weight loss as fat free mass) (21–23) when compared to daily CR (75% weight lost as fat, 25% weight loss as fat free mass) (4,7–16).

So on a standard diet, the typical composition of weight loss is 75% fat / 25% muscle, while it appears to be 90% fat / 10% muscle on intermittent fasting based regimens. You don't have to be a rocket scientist to understand that this is quite amazing if true.

Now, here's where it get a little bit strange. I just talked about factors that affect muscle retention during weight loss: exercise, body fat and diet. It seems that the author doesn't take any of these factors into account when he states he provides the figures 90% / 10% and 75% / 25% for IF and CR respectively.

A few of the CR trials that were used to arrive at the 75% / 25% figure included exercise, one included growth hormone administration and another one used a high-protein diet. Only one of the IF trials included exercise.

As you may understand, this is a major weakness when attempting to formulate a good estimate of the amount of weight lost and fat and muscle respectively. While the author is aware of this, he briefly skims over the issue (in the discussion), saying that results may vary depending on subject population, etc., but it is truly a major weakness of the paper and its conclusions:

For instance, findings between trials may have varied based on the different populations used for each study. The trials reviewed here differed greatly in terms of subject age range, inclusion of one or both sexes, and BMI classification. Thus, it is possible that the discrepancy in effects observed between studies could be partly due to the subject population employed. Results between studies may have also varied depending on the different feeding protocols utilized.

Strangely there is no mention of the exercise regimens that were used in a few of the CR-trials.

Furthermore, as if there aren't enough confounders present as it is, there's the issue of how body composition was measured. In order to assess and track changes in body composition during weight loss studies, researchers use different methods of measuring. The most basic method of tracking changes in body composition involves a pair of calipers in the hands of a professional, but this is not commonly used nowadays. Instead, body composition is usually measured by bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry (DXA) and magnetic resonance imaging (MRI).

Without going into a lot of technical detail, there is a lot of variance in terms of how precise each one of these methods are. Though BIA is regarded as "good enough" to use in clinical trials, DXA and MRI tend to be a lot more accurate. And therein lies the problem; a larger percentage of the intermittent-fasting-based trials used BIA, while many of the CR-trials used DXA or MRI. If tracking methods differ between trials, it obviously skews the results.

Although the data are limited, preliminary findings indicate that individuals may find it easier to adhere to intermittent CR when compared to daily CR for short treatment durations (i.e. 12 weeks) (22). Whether or not this improved adherence to intermittent CR can help people with long-term weight maintenance is an important issue that warrants further research.

Well, that's certainly something most of us can agree with. Pretty much all of my clients convert to intermittent fasting once they try it. I haven't actually heard from anyone that went back to high-frequency meal patterns again.

Here's the conclusion:

In sum, intermittent CR and daily CR diets appear to be equally as effective in decreasing body weight, fat mass, and potentially, visceral fat mass. However, intermittent restriction regimens may be superior to daily restriction regimens in that they help conserve lean mass at the expense of fat mass. These findings add to the growing body of evidence showing that intermittent CR may be implemented as another viable option for weight loss in overweight and obese populations.

Note the "may be". As I pointed out earlier, the study review has weaknesses that makes it hard to treat it as concrete evidence of a muscle-sparing effect.

Personal Observations

One thing that always stood out to me in working with clients was the fact that they were able to keep all their muscle - even while dieting to very low body fat percentages. I'm talking about clients with years of weight training experience dieting to 5-6% body fat. They either gained strength and muscle mass or were able to maintain strength and muscle mass perfectly. I'm not talking about Average Joe Beginner Client with a blurry two-pack losing a few pounds while gaining muscle (AKA "newbie magic"). I've had the same experience myself.

46-year old Dan was one of many clients from my latest client update that gained strength despite losing substantial amounts of body fat during his diet (-35 lbs in his case). I've had natural bodybuilding competitors setting personal records two weeks before the stage. Perhaps there is something to the muscle-sparing effects of intermittent fasting?

Numerous Leangains followers and success stories have also attested to the muscle-sparing effects of intermittent fasting. They have shared their experiences in the intermittent fasting thread on bodybuilding.com, in blog comments, in emails, on Twitter, my Facebook wall, forums, and other places. If this counts as any sort of evidence, it's easy to find.

Obviously, it's damn near impossible to say something for certain based on anecdotes. As I noted with the tracking methods in the review just discussed, there are often major confounders present.

Was it the switch to intermittent fasting that produced the favorable effect or was it the change in training and diet? Perhaps protein intake was increased.

Maybe the person in question ditched his high-rep pump'n'tone BS routine and replaced it with a sensible training routine like Reverse Pyramid.

All of this makes self-reporting and anecdotes dubious methods for drawing definite conclusions. But let us for one second entertain the thought of a muscle-sparing effect of intermittent fasting: the sheer amount of evidence, even if weak when viewed in isolation, suggests that there might be something to it.

This would then beg the question: why is intermittent fasting superior for preserving muscle mass during weight loss? What is the mechanism? That's a topic for another time and another article.

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comments:

Great post, keep up the great work! I would like to point out that the leangains protocol is not intermittent fasting, but actually regular fasting. Intermittent literally means with irregular intervals, but fasting everyday from 8pm to 12pm is very regular and not intermittent at all :)

For whatever it's worth, I've dropped almost 7kg (from 89-90 to 82-83) since New Years using an IF approach with keto-style protein and fat foods.

Strength has (mostly) maintained itself despite training with the 'excessive' volume I've become a fan of in the last year. But volume in my terms means the Bulgarian/Russian sense -- lots of big lifts with very low reps, not so much pump 'n tone (though I still pump my guns once a week on my carb-up day).

Regardless of the findings, the people that follow this site and even my own have been experiencing significant fat loss with maximum muscle retention.Some times the real world results speak so much volume that the actual papers are merely a supporting token :)

@Shawn - Actually intermittent is the correct word, it means ceasing for a time and beginning again, and can be used to describe either regular or irregular intervals. Look up more than one internet definition and you'll see that.

Secondly, great article! Hopefully there will be more cohesion in future research into fasting and more focus on the inclusion of exercise. I suppose these studies are for the benefit of the lazy obese rather than those looking for sub 10 bf.

I've been scanning through your blog for the last few days and I think it's great I'll definitely be giving this a try.. it makes perfect sense to me!

I have 2 questions that I'm wondering about, maybe you or somebody else in the know could answer.

1. regarding eating before bed-time. I will likely be best suited to use the 4 - 6 PM to 12 - 2 feeding schedule, but traditionally it's said that one should not eat 2 or 3 hours before bed. I'm sorry I haven't been able to find anything specific on your website about this and wanted to know what you know about wether eating before bed is as bad as "they" say.

2. I work nights, so the late eating window would be good for work days, but on my days off I usually do a lot of things like hiking, biking and snowboarding which are usually all day things, and just that, in the day. should I be adding nutrition to my days to sustain these activities?

I've been on IF for 10 weeks now, increased my lean body mass slightly, and lost about 2kg of fat - and the only change I've made to my diet was to increase protein intake and add BCAAs (20g on training days, 5g on off-days)!

I'm now starting to cut down on calories, and would be very grateful on how much should I cut and what. I'm of course getting rid of most sugar, bread and milk products.

Great post. Very refreshing to see such objectivity and professionalism. So rare in the guru biz. Your qualities - knowledge, honesty and real world experienece - makes you one of a kind, Martin. A donation is on the way, much deserved I should add. Keep up the great work.

You truly are the guy with the Camel Boots - a guy walking tall on his own path... and the rest of us mortals trailing after you.

You're doing great work getting the word out, it is much appreciated.

Also, thanks for the link to your previous article on the RPT - lately I've been shifting from 5x5 to this mentality and wondering how it would fit my training and diet. Seems like I was intuitively on the path and you just verified it. :)

Much kudos (och respekt) to you overall and I'll be sure to grab your book (once you decide to publish it).

Thanks for all the great articles but...I take issue with this analogy:"No need to touch the emergency funds (muscle protein) if you have money in your savings account (adipose tissue)."

If you think of your body as a factory with adipose tissue being cash reserves and muscle protein being the workforce it makes more sense. Short term income problem > use reserves (fat), long term income problem > fire workforce (muscle).This analogy has problems too of course since must pay energy to keep our fat stores and we gain some energy from burning muscle but overall it's better (IMO).

Since you're a huge internet guru now I was fulling expecting you to pimp the fuck out of your method in this article, yet you remained objective and critical throughout. Something you just don't see very often. Good shit brah

Great post Martin. was kind of hard to understand fully due to the vast amount of scientific language, but i got what you were talking about.

Shawn, I don't think that everybody who does IF fast every day in the same hours, I'm sure that a lot of people here fast differently through the week. I for example change my fasting period regarding of what my daily schedule is.therefore you can actually say that this method is considered as Intermittent.

Martin, do you severely restrict calories in the eating phase? I might unintentionally hit only 1300-1400 (lower-carb) calories a day during my feeding time, but I think when done long-term this might be too low? I am 5'4, ~112lbs, lift heavy things around 2-3x a week and bike several miles a week. I am not trying to lose weight. How do you estimate caloric needs?

Like the others pointed out it was awesome to see you keep it real...despite it might have served you better to not critique the study at all:) Speaks tons about your credibility IMO. Great stuff as always Martin. Leangains FTW!

@Ahem, (an) Anonymous, Jess, Timothy - why bother asking questions like that? a) the answer is already provided by the leangains guide or b) you haven't given enough info to answer anyway, everyone's individual. I'd wait for the book like the rest of us or hit Martin up for personal training.

Even Herschel Walker does intermittent fasting, without even knowing he's doing it. He eats only one big meal a day at around 8-9 PM, and has been doing this for over 20 years with great success/ results.

The dude is in his late 40's and looks like he's in his early 30's and competes in mixed martial arts. He's totally shredded and huge!

You can hear his interview about his eating habits here:http://www.youtube.com/watch?v=5odKC4x-61E

Martin, about your twitter-comment on the study of increased fat-oxidation from ingesting catechins+caffeine. I read the abstract but couldn't figure out any amount of catechins and caffeine that would significantly increase fat-oxidation, and how that would translate into cups of coffee and green tea or green tea supplements. Do you have any thoughts?Hope the day are as sunny in Malmö as they are here in Stockholm, and the parks have started to blossom!

Excellent post. You said you were doing monthly research reviews for a Swedish magazine - any chance of these getting translated? I would very much like to read them (and so would many others I'm sure).

This doesn't really belong here, but it came to my mind reading your older posts (Definition of Lean Gains, with the Paleo-oriented dude) and I was thinking to ask you what I'm sure's been asked before but I've not yet found the answer:

During workout days it's good to go over maintenance with calories if I'm looking to put on muscle. How should I take in those calories? For paleo people tend to recommend upping fat intake. What's your take on this? If you eat leangains-style huge carb/protein meal after a workout, and about two-three hours afterwards you still need to get about 500kcal in, what would you eat? I've been doing a mixture of Quark, whey and a handful of almonds to up the calories.

Are any of your clients predominatly involved in sports conditioning rather than body buidling?

I've been following your approach for a couple of months and am definately more lean. However I am struggling with energy and elongated DOMS for and after MMA/boxing training and conditoining. I usually strength train once a week and do condioning twice alongside technical sessions. I'm following BMR+20% for training days and BMR-20% on rest days. Any brief thoughts on your expereince greatfully received! Thanks,

Just a quick question about training, would it be OK to do the Starting Strength beginner program but replacing power cleans with chins? Also is it fine to just do it 2x/week instead of 3x/week, for better recovery (I'm a lazy fuck) So it would be like this:

Hi Martin! Just thought you might be interested by this. Herschel Walker, one of the most unbelievable athletes of all time mention in this interview how he only eats once a day. Also boxer Chris Eubank mentions the same thing in his autobiography. Of course these have no scientific relevance whatsoever but still interesting.

"Note the one study that is not published yet and includes exercise. I'm very much looking forward to seeing that one. It would be interesting to see what kind of exercise regimen they are using. I'm hoping it's weight training."

I'm hoping the same, but it looks unlikey, judging from the author's comment on page 7 of the paper (just before the conclusions begin), where they state: "As endurance exercise has been shown to selectively reduce visceral fat mass and ain in the retention of lean mass (42), the combination effects of these two interventions on body weight and body composition could be a fruitful area of future study".

This is completely off-topic, but I simply have to ask you this certain question. My friends and I have been debating this quite a while.

Your physique is outstanding, especially your biceps, but what I am really curious about is whether you do chest dips. Do you? Do you do any more exercises than the big 4 (Bench, Dead, Squat, Chin)? I ask this because I see a significant lack of development in your triceps (compared to the rest of your physique). I mean yes, they get worked during bench pressing, but to the same extend biceps get worked during bent-over rows (not that much).

Hi, Martin nice blog, but no book and no personal consultations. How am I going to give IF a try?. I´m sure there is more to it than the leangains guide, if not, what´s the reason of writing a book about it?

I'm really eager to try IF but I need more tools to do it than just the leangains guide.

Question though: If i want to do a separate cardio workout during the day, for example if being involved in some sort of sport besides strength- training or just enjoys running as exercise, when do you recommend this workout should be done if you use:

You gotta get that book out. People are publishing a bunch of repetitive bullshit prematurely about IF that you are giving away for free on your blog. And they are charging shitloads for it. It's pretty ridiculous. None of them are doing half the research you are.

Excellent Blog and Articles. I am just working out intergrating Leangains into my situation.

At 5'8" I sit at 165 and estimate (based purely on picture compariso) my BF to be in the 15% ballpark. recomp is therefore my priority (to state the obvious).

Lame excuses follow as im sure people following your system work longer and harder than I, but I commute every day and am therefore away from the house from 6am to 6.00pm. I wake at 5.30am train (3 times a week) around 7pm and retire at 10pm. I appreciate I dont get enough sleep but with a 2 year old girl and household responsibilities I will find it difficult to retire before 10pm (again sorry to make excuses)

My question therefore is can i extent the fast to 20 hours for convenience as then id not need to pack any food for the day. This assumes the following is in check:

Quick Question. I just did some lifting this morning in my fasted state and am still fasting now. I'll eat in an hour or so, which which will put my fast around the 16 hour mark (give or take).

I'm a firm believer in IF and even in the Pilon method (24 hour periods). After a good day of lifting Monday (today is Wednesday) I've noticed that I'm a lot stronger than I thought I was and now need to buy some heavier weight (I do all my workouts at home with dumbbells).

Question is: What's better? To break the fast 15-45 minutes after the workout to replace glycogen stores or just keep the fast going for the full 16 hours? I'm not looking to bulk up at all in the foreseeable future, but I don't want to lose strength (or become anorexic) and want to keep adding weight at regular intervals (though it doesn't need to be every week - I'm in no rush). I'm in this for fat loss, getting cut and having optimal nutrition. Aside from a general caloric deficit, am I running any risks by not eating solid food for another 2 or 3 hours after the workouts?

I've been exercising regularly for close to 14 years now (am 30 years old) so the weight training itself is not a shock to my system, but it's only in the last few months that I realize how much more progress I could have been making with a few simple tweaks. I just don't want to over-tweak (something I'm exceptionally good at).

If it means anything: I am 6'3" (191cm), Roughly 154 lbs (70.1 kilos at last weigh in - I think I'm too light already and need to eat more), wide shoulder, thin waist...mostly a mesomorph frame with the lower body of an ectomorph (mostly) and some slight endomorph tendencies if I make the wrong food combinations. STUBBORN belly fat. (though it's coming off pretty easily with IF).

I should ask, and I'm sorry if this was already answered elsewhere, but what are your thoughts about having ingested a slow release protein shake before bed? I usually have this between 9 and 10 pm and then awake at 5am. I don't consume anything until about 5:30pm(so far - I'm new to IF, but not traditional fasting) starting with post w.o. shake w/creatine and first meal within the hour. I guess that brings forth a second question: Is this too long of a fasting window?

I've only been having earlier calories on leg day(a protein blend shake of fast and slow release with a couple tbl spoons of milled flax seed) at anywhere from Noon to 3pm. Should I have a "normal" before workout meal with my early rise time and late afternoon training? Note: I hit the sack between 9 and 10pm.